The present invention generally relates to actuators for valves, for example external actuators for valves such as butterfly valves.
Actuators for valves, such as butterfly valves, are well known. In some arrangements, a drive screw is rotated to cause a traveling nut to move a crank arm attached to the valve axle to rotate the valve member into and out of engagement with the valve seat.
In the case of a butterfly valve, the valve member is rotated approximately 90 degrees between an open position and a closed position. The precise closed position may change over time as the valve seat wears, or as conditions require greater or lesser closing force of the valve member against the valve seat. Typically some type of abutment occurs between the traveling nut and a fixed nut carried on the drive screw, as shown in U.S. Pat. Nos. Re. 29,253 and 3,147,766, or between the crank arm and an adjustable stop, such as a screw projecting through a wall of the actuator body, as shown in U.S. Pat. No. 3,385,120.
Screws projecting through the actuator body are not useful for large valves in that the torques required to close the valve either cause failure of the body wall at the location of the screw penetration, or require an overly thick wall at the penetration point, increasing the cost of the actuator.
The use of adjustable stop nuts located in the interior of the actuator body requires the body to be opened to make adjustments to the stop positions. Usually the interior of the actuator body is filled with grease making the adjustment a messy operation, but also, the operation is time consuming in that the actuator body must be opened, the nut located and cleaned to provide access, a locking pin must be located and driven out of the openings where it is located, generally in tight quarters, the nut rotated to a new position, the pin re-driven into the openings, again in tight quarters, grease repacked into the interior, and then the body being sealed closed. This is often a trial and error process requiring the body to be opened more than once.
U.S. Pat. No. 3,575,378 discloses a sleeve 36, secured axially in place on the drive shaft 13 by stop collars 43 and 44. The sleeve 36, and drive shaft 13 are held in an exteriorly adjustable position by a setscrew 41. The setscrew 41 may be loosened to allow an axial repositioning of both the sleeve 36 and the drive shaft 13, but does not allow for adjustment of the sleeve relative to the drive shaft from the exterior of the body. The setscrew 41 must hold against the closing force of the nut 16 driven by the drive shaft 13, however, a side pressing setscrew is not capable of providing support against 450 ft-lbs of load often created in closing large butterfly valves. Further, the setscrew 41 transfers the load created by the press of the nut 16 against the collar 43 directly to the fixed support portion 35 of the housing 20, requiring a substantially thickened housing wall.
U.S. Pat. No. Re. 29,253 provides a collar 60 which defines an end stop 66 for the operating nut 100 carried on the operating shaft 28. The collar 60 is exteriorly adjustable, relative to the housing 26 via a threaded connection 58 with the housing, however, the collar is positionally fixed relative to the operating shaft 28 via a retainer nut 80 holding a stem bushing member 76 against the collar, with the stem bushing member being pinned to the operating shaft 28 at 78. Thus, when the position of the collar 60 relative to the housing 26 is changed, the axial position of the operating shaft 28 is also changed, and the axial position of the collar cannot be adjusted relative to the operating shaft from the exterior. Further, the load created by the operating nut 100 pressing against the collar 60 or the stop 50 is transferred directly to the housing 26 via the threaded connection 58 of the collar with the housing.
U.S. Pat. Nos. 4,146,050, 3,262,535 and 1,406,748 show various types of externally adjustable sleeves for different types of valves.